The present invention relates to compact electronic modules, and to components and packaging for use with such modules.
One of the long-term trends in electronics has been to provide higher functionality at lower cost in a more compact package. Many pages have been written on this long-term trend, and it will not be analyzed here. However, the numerous innovations disclosed in the present application are believed to contribute to a major advance in this direction.
Innovative Module
The present application discloses a very compact electronic module, which includes an integrated circuit (preferably including memory) and a batter. The module is preferably coin-shaped, and the two fare of the module are isolated from each other. Host system can read/write such modules, by using a one-wire-bus protocol.
One-Wire-to-Three-Wire Converter
The module may contain one integrated circuit or several but the integrated circuits in the module preferably include a one-wire-to-three-wire converter circuit. In the presently preferred embodiment, this is integrated on a single chip with small amount of serial-access memory. However, alternatively the converter may be used to provide a standard three-wire serial bus output, which provides an interface to one or more other chips. The other chips may include, for example, electronic keys (such as the DS1207 from Dallas Semiconductor).
ESD Protection Needs
A common specification for integrated circuits is the ability to withstand five successive electrostatic discharges (ESDs), each of 1000 volts, at the circuit pads, without the leakage current increasing to 1 microAmpere. However, a de facto standard of 2000 V ESD immunity has been springing up for many applications.
However, even this level of ESD immunity may be insufficient for high-noise applications. Specifically, in the large-scale systems environment of the presently preferred embodiment, the data modules will face some unusual integrity requirements. Since the modules may be exposed to very rough treatment, in consumer and industrial environments, they should preferably have a very high level of immunity to electrostatic discharge (ESD).
The electronic data module of the presently preferred embodiment includes an innovative ESD protection diode structure, which helps to protect against data loss under severe electrostatic discharge conditions.
Innovative Packaging Scheme
To fit the integrated circuit into this very small space, an innovative packaging scheme is used in the preferred embodiment. A two-part metal container is used, which has two shallow concave pieces which fit together. The integrated circuit (preferably in a low-height package, such as a flat-pack or small outline integrated circuit (SOIC) is mounted on a very small printed circuit board (preferably a flexible board), which fits inside the container. Laterally spaced from the integrated circuit, on the other end of the small board, the board end is sandwiched between a battery and a piece of elastic conductive material (such as conductive plastic foam). Thus, the battery is connected between one face of the container and a power conductor on the board. The piece of elastic conductive material makes contact between a data trace on the board and the other face of the container. Another trace on the board makes contact directly to the container face on which the battery's ground terminal is connected. Thus, simple wiring on the small board, using through-hole visa, suffices to route power, ground, and data lines to the integrated circuit, while providing a sealed durable package with two external contacts.
The battery is preferably a low-voltage battery (1.5 V, in the preferred embodiment.) This is cheaper, and maximizes power efficiency, but requires some innovative circuit design features to accommodate the electrical interface. (Electrical watches have often been powered by 1.5 V batteries, but such devices do not have any direct electrical interface to the outside world. By contrast, the module of the presently preferred embodiment communicates over a one-wire bus which is driven by full CMOS voltage levels.)